Gas bubble mixers for improving the performance of anaerobic digestion of waste sludge, are known in the art. Such gas bubble mixers generally comprise two main components; namely, a large stack pipe and a gas piston-bubble generator (hereafter referred to as a “gas bubble generator”) that is located adjacent to the stack pipe.
In use, both the stackpipe and the bubble generator are completely submerged within the body of waste sludge, with the stackpipe positioned in a vertical configuration. The stackpipe has a liquid intake opening at its base and a gas/liquid discharge opening at its upper end. The stackpipe further includes a gas bubble inlet at its lower end that is in communication with the gas bubble generator. The gas bubble generator is thus operative for producing gas bubbles that are supplied to the stackpipe through the gas bubble inlet.
Gas bubble generators typically include gas accumulation chambers in which gas is received from a gas supply line, and a stand pipe through which the accumulated gas exits the bubble generator into the stackpipe. Once a sufficient amount of gas has accumulated within the gas accumulation chambers, the gas is naturally siphoned out of the bubble generator through the stand pipe and into the stackpipe, thereby forming a large gas bubble within the stackpipe. As this bubble rises, it creates a piston-like effect that both pushes and pulls the liquid containing dissolved and suspended solids upwards through the stackpipe. By effecting this simultaneous two-phase flow, the gas bubbles that travel through the stack pipe produce a strong pumping action, which continually mixes the body of liquid. This continuous mixing aids in the anaerobic digestion process of transforming organic solids into a gaseous state by maintaining a uniformity of the incoming solids within the mixture, and by helping to maintain the body of liquid at a constant temperature.
Although gas bubble mixers of the type outlined above are known in the art, most gas bubble mixers that are currently in use today contain many deficiencies that render them inefficient and difficult to work with.
One of the major deficiencies with existing gas bubble mixers is that they often get clogged after start-up, and are then very difficult and inconvenient to clean. Keeping in mind that most gas bubble mixers are placed in large tanks of waste sludge that contain organic solids and a smaller portion of non-biodegradable solids such as grit, hair, paper, plastics, small stones, sand, and other difficult-to-degrade debris, it is not surprising that after a period of use this debris gets inside the gas bubble mixers and causes them to clog. Obviously, when such clogging happens, the bubble generators need to be cleaned out and unclogged so that they can return to normal function. While some bubble generators include flushing passages that are able to flush out and unclog some of their chambers, there are many parts of the bubble generators that can only be cleaned out by emptying the tank of the waste sludge, and then manually cleaning out the bubble generators. This cleaning process causes significant expense due to the effort required to empty the tank, as well as the significant down-time caused by this cleaning, during which time the anaerobic digestion system is not in use.
A further deficiency with existing bubble generators lies in their inefficient bubble generation. Due to the size and internal configuration of many bubble generators, they create bubbles that are either too large or too small to effectively create an efficient and effective pumping action through the stackpipe. Producing bubbles that are too large renders the system inefficient, since it increases the energy costs associated with the operation of the bubble mixers, and producing bubbles that are too small yields inadequate pumping action.
A further deficiency with existing bubble mixers lies in their poorly designed hydraulic braking orifices. Many existing bubble mixers are ineffective at producing adequate gas bubbles due to poor bubble frequency control. If the frequency of bubble emission is not properly calibrated, the accumulated gas volume within the bubble generator will either break into many smaller bubbles on entry into the stackpipe or it will generate an inefficient, fluctuating pumping action. Both scenarios cause an ineffective pumping action and poor liquid circulation through the stackpipe. Furthermore, hydraulic braking orifices that are positioned between the second gas accumulation chamber and the stand pipe often create incomplete flushing of the gas contained within the gas accumulation chambers. This incomplete flushing can lead to debris deposition and build-up inside the gas accumulation chambers and the stand pipe, which will cause clogging to occur more rapidly.
A still further deficiency with many gas bubble mixers is that the stackpipe is supported with supporting legs that surround the stackpipe's liquid intake opening. The congestion caused by these supports restricts liquid flow into the stackpipe. This in turn can prevent the gas bubble mixers from effectively and uniformly mixing the liquid/waste sludge contained within the tank.
In light of the above, it can be seen that there is a need in the industry for a gas bubble mixer that integrates an improved gas bubble generator that alleviates, at least in part, the deficiencies of the prior art, and improves on the overall efficiency of the gas bubble mixer.